This relates generally to wireless displays.
Wireless display technology generally involves a source which transmits data for display on a sink such as a monitor or display device. Most sinks today only work in the landscape or sideways mode. Current wireless specifications have tended to not address the rotation problem explicitly.
In fact, version 1.1 of the WiFi Display Technical Specification (2012) (available from Wi-Fi Alliance) only allows for landscape mode (landscape first mode) to be transmitted over the air in all scenarios and rotation is largely ignored. Several scenarios have come up that require a more explicit definition: 1) Portrait-first displays (displays that scan content in portrait order) are increasingly common, 2) Sink devices allow for windowed or docked mode of operation i.e., device orientation could be different than content orientation, 3) a single Source could be transmitting content to more than one Sink—and some of the Sinks could be rotated while others are not, 4) the Source itself could be rotated, 5) content in the Source could have either Landscape or Portrait orientation, and 6) many of the Sinks (e.g., TVs, or notebook computers or tablet devices) have Graphics Processing Units (GPUs) in them that allow them to transform received content if the framework allows it.
A naïve implementation could result in source content being aspect ratio scaled twice. It may be scaled once for a landscape presentation and then another time for a portrait presentation, resulting in suboptimal output at the display.